Home > Engine Family >

Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp OHV, Stage 2.5
Hop Up Kit - GX340 - GX390, 420 Predators, and 13/15hp OHV, Stage 2.5

Our Price: $449.99

Stock Status:In Stock
Part #: STAGE3KIT390

Choose Engine Type

420 Predator OHV
Select Carburator

GX390 Bored - Gas
GX390 Bored - Methanol
34mm Flat Slide Mikuni - Gas [+$81]
33 Mikuni Pumper - Gas [+$195]
33 Mikuni Pumper - Methanol [+$271]
Header & Exhaust Options

No Exhaust
Add Header, Kart & Mini-Bike [+$35]
Add Header, Muffler, and Clamp: Kart & Mini-Bikes [+$71]
Add Mud Motor Header & Muffler (390) [+$40]
Select Rocker Arm Type

1.2 Billet Roller Tip, includes CM Pushrods [+$85]
Roller (includes spacer) [+$179]
Select Camshaft

280 RPM (Med to large tracks, 7000+ )
280 TQ (Hi Torque, Small tracks, 6000 rpm)
280 Marine (Super Low end,5000 rpm)
Select Flywheel

No Flywheel
Add Aluminum Flywheel - Recoil Start [+$166]
Add Aluminum Flywheel - Electric Start [+$202]
Additional Options

Add UT2 Coil w/o Rev Limiter, for UT2 Hondas Only [+$63]

Add Genuine Honda UT1 Coil [+$32]

Description -

As step up from the Stage 1, this kit is designed to improve the power for the GX340s and GX390s along with improving the durability.


Race/Open Air Filter & Adapter

  • Choice of Carbs
  • HD Valve Springs
  • Offset Timing Key
  • 280 Lift Cam
  • Reinforced Rockers (not included on Hemis)
  • Billet Rod +(.040 longer)
  • Carb and Side Cover Gaskets
  • Optional Header/Exhaust
  • Optional Aluminum Flywheel

Picture for reference only and may show optional parts. See above description for actual content.
Header not included unless specified.

Note: Use of the Choke Bracket requires use of a stock Honda (or Chinese OHV) "Air Filter to Carb Gasket". This is not included in the kit. You can use the one that came with the motor, or can purchase one at

Filter should be sprayed with K&N type oil, especially in dirt applications. Oil not included click here

Billet Aluminum flywheel recommended. Stock flywheels, esp "Clone" are prone to failure and very DANGEROUS

Note: UT2s series Hondas (2012 & up) or later have a built in Rev Limiter in the coil and will require a new coil to exceed 4000 rpm. The UT2 coils (4 wire) can only be used with stock flywheels.
If using a Billet Flywheel, you must run a UT1 style coil (single wire).

13/15 Chinese Engines (414, 420, 460) usually have UT1 style coils already. However some Lifans and 420s have a digital ignition and will need a Honda UT1 coil to run t he billet flywheel

Share your knowledge of this product. Be the first to write a review »